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PREAD
Section: Linux Programmer's Manual (2)
Updated: 2010-09-20
Index
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NAME
pread, pwrite - read from or write to a file descriptor at a given offset
SYNOPSIS
#include <unistd.h>
ssize_t pread(int fd, void *buf, size_t count, off_t offset);
ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
pread(),
pwrite():
-
- Since glibc 2.12:
-
_XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200809L
- Before glibc 2.12:
-
_XOPEN_SOURCE >= 500
DESCRIPTION
pread()
reads up to
count
bytes from file descriptor
fd
at offset
offset
(from the start of the file) into the buffer starting at
buf.
The file offset is not changed.
pwrite()
writes up to
count
bytes from the buffer starting at
buf
to the file descriptor
fd
at offset
offset.
The file offset is not changed.
The file referenced by
fd
must be capable of seeking.
RETURN VALUE
On success, the number of bytes read or written is returned (zero
indicates that nothing was written, in the case of
pwrite(),
or
end of file, in the case of
pread()),
or -1 on error, in which case
errno
is set to indicate the error.
ERRORS
pread()
can fail and set
errno
to any error specified for
read(2)
or
lseek(2).
pwrite()
can fail and set
errno
to any error specified for
write(2)
or
lseek(2).
VERSIONS
The
pread()
and
pwrite()
system calls were added to Linux in
version 2.1.60; the entries in the i386 system call table were added
in 2.1.69.
C library support (including emulation using
lseek(2)
on older kernels without the system calls) was added in glibc 2.1.
CONFORMING TO
POSIX.1-2001.
SEE ALSO
lseek(2),
read(2),
write(2),
feature_test_macros(7)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- SEE ALSO
-
- COLOPHON
-
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